1. Field of the Invention
The present invention relates to a method of printing a calibration pattern for use in calibrating a printer, and also to a printer having a function to print a calibration pattern.
2. Background Arts
In a thermosensitive color printer, thermosensitive color recording paper, hereinafter called simply the recording paper, is directly headed by a thermal head. The recording paper has thermosensitive coloring layers formed atop another, for developing a different color from each other. The coloring layers have different heat-sensitivities from each other that decrease with the depth or distance of the respective layers from an obverse surface of the recording layer. Because of the difference in heat-sensitivity between the three coloring layers, it is possible to record three color frames sequentially from the most sensitive coloring layer to the least sensitive coloring layer by applying increasing amounts of heat energy (mJ/mm2) to the recording paper from one color after another. The coloring layer having a color frame recorded thereon is fixed by electromagnetic rays of a specific range before recording the next color frame, so the already colored layer is stopped from being colored unnecessarily by the heat energy applied for the next color.
Because the sensitivities of the respective coloring layers and the heat energies applied from the thermal head vary unexpectedly depending upon production tolerances, environmental conditions, such as temperature and humidity, and aging of the printer, variations in color balance and gradation of printed image are inevitable in the thermosensitive color printer. To achieve a high fidelity, it is desirable to calibrate the printer before printing as frequently as possible.
For calibration, a calibration pattern consisting of yellow (Y), magenta (M) and cyan (C) segments or that having a gray segment in addition to these three color segments is printed to produce a test print. Then, densities of the respective segments of the test print are measured by a densitometer. On the basis of deviations of the measured densities from reference values, correction values are calculated, and are used for correcting color balance or density of the printer so as to compensate for the deviations.
However, since the conventional calibration method needs to select a calibration mode and make special and labor-consuming operations, or requires specific skills, it has been difficult to perform calibration regularly in terms of cost and time-efficiency.
Furthermore, since the test print wastes the recording paper, frequent calibrations would result in increasing the waste of recording paper.
In view of the foregoing, an object of the present invention is to provide a method of printing a calibration pattern that makes it possible to perform calibrations regularly with high efficiency while reducing waste of recording paper.
Another object of the present invention is to provide a printer that can print a calibration pattern according to the method of the present invention.
According to the present invention, for a printer that prints an image in an image recording area on a recording paper, a calibration pattern printing method comprises the steps of: printing a calibration pattern in a marginal area on the recording paper outside the image recording area; and cutting the marginal area with the calibration pattern off the recording paper after the image is printed in the image recording area.
For a printer that is loaded with a roll of recording paper, a calibration pattern printing method according to the present invention comprises the steps of: printing a calibration pattern on a leading end portion of the recording paper; and cutting the leading end with the calibration pattern off the recording paper.
Since the calibration pattern is printed on a leading end portion or a margin that is to be cut off regardless of whether the calibration pattern is printed thereon or not, the waste of recording paper is not increased by printing the calibration pattern. Also, it becomes possible to design the printer to print and measure the calibration pattern automatically at predetermined timings.
Where a plurality of the image recording areas are provided in predetermined positions on the recording paper, it is preferable that the method of the present invention further comprises the following steps: detecting a leading end edge of the recording paper as being conveyed through the printer; detecting the positions of the image recording areas; determining a first preliminary cutting position for cutting off the leading end portion on the basis of the position of a nearest one of the image recording areas to the leading end edge; comparing a length from the leading end edge to the first preliminary cutting position with a reference value that is defined by a requisite printing area for the calibration pattern; and cutting the leading end portion, if the length is less than the reference value, at a second preliminary cutting position that is farther from the leading end edge by one image recording area than the first preliminary cutting position.
A printer of the present invention, that prints an image in an image recording area on a recording paper with at least a margin outside the image recording area, comprises: a device for supplying a printing head with data for printing a calibration pattern on the margin; and a device for cutting the margin off the recording paper after the calibration pattern is printed on the margin.
According to another aspect of the present invention, a printer for use with a roll of recording paper comprises: a sensor for detecting a leading end edge of the recording paper as being conveyed through the printer; a cutter for cutting off a leading end portion of the recording paper before an image is printed on the recording paper, and for cutting the recording paper into a piece with the image printed thereon; and a device for driving a printing head of the printer to print a calibration pattern on the leading end portion after the sensor detects the leading end edge before the cutter cuts off the leading end portion.